1. Field of the Invention
The present invention relates to a microprocessor-incorporated vehicle engine control system in which, in order to rapidly drive the fuel-injection electromagnetic valve of an internal combustion engine, a boosted high voltage is instantaneously supplied from a vehicle battery to the electromagnetic coil for driving the electromagnet valve and valve-opening holding control is performed by means of the voltage of the vehicle battery; in particular, the present invention relates to a vehicle engine control system in which while the high-speed control load on the microprocessor is reduced, the control accuracy in fuel injection is raised.
2. Description of the Related Art
It is widely put into practice that for a plurality of electromagnetic coils that are provided at the respective cylinders of a multi-cylinder engine and drive the respective fuel-injection electromagnetic valves, a microprocessor that operates in response to the output of a crank angle sensor sequentially and selectively sets the respective valve opening and valve closing timings, and hardware provided outside the microprocessor performs rapid excitation control and opened-valve holding control so that rapid opening and opened-valve holding of the electromagnetic valve are implemented.
In general, in such an existing vehicle engine control system, the excitation current for the electromagnetic coil is monitored through an analogue signal voltage obtained by amplifying the voltage across a current detection resistor connected in series with the electromagnetic coil, and as the hardware provided outside the microprocessor, an analogue comparison circuit generates a logic signal for control. In this case, the comparison determination threshold value to be inputted to the comparison circuit is generated based on an analogue reference voltage; therefore, it is difficult for the microprocessor to correct the comparison determination threshold value.
However, there is publicly known a vehicle engine control system utilizing a method in which the detected signal voltage obtained from an excitation current is digital-converted by an A/D converter and a comparison determination threshold value is digitally set. For example, Patent Document 1, listed below, discloses a fuel injection valve control apparatus that makes it possible to implement stable fuel injection even when the voltage of a vehicle battery fluctuates and to implement limp-home operation against the abnormality in an opening/closing device or an auxiliary power source that generates a boosted high voltage.
According to FIG. 1 in Patent Document 1, the voltage across a current detection device (current detection resistor) 29 connected in series with an electromagnetic solenoid (electromagnetic coil) 27 is inputted to an A/D converter 32 by way of an amplifier 31; in response to a valve opening signal (valve-opening command signal) PL1 generated by a microprocessor 4a and the present value of an excitation current that has been digital-converted by an A/D converter 32, a logic circuit 16 generates control signals A, B, and C; then, as represented in the timing chart of FIG. 2, a first opening/closing device (high-voltage opening/closing device) 20 implements rapid excitation control, a second opening/closing device 24 implements opened-valve holding control, and a third opening/closing device (selective opening/closing device) 28 implements selective conduction and rapid cutoff control.
On the other hand, there is also publicly known a technology of monitoring the generation condition of a rapid excitation current in a typical vehicle engine control system utilizing a method in which the detected signal voltage obtained from an excitation current, left as an analogue signal, is utilized and a comparison determination value is set with an analogue value. For example, Patent Document 2, listed below, discloses a technology in which according to FIGS. 3 and 5, a fuel injection control apparatus is provided with switching devices 50, 51, and 52, a current detection resistor 60, a fuel injection valve drive IC56, and an engine control unit ECU19.
In response to a valve-opening command signal generated by ECU19 and a current detection signal voltage obtained through the current detection resistor 60, IC56 in Patent Document 2 closes the switching devices 50 and 52 based on a valve opening command of the injection pulse width Ti. The value of an excitation current at a time when a circuit-closing drive time Th has elapsed is compared with a target peak current Ipeak, which is a predetermined determination threshold value; in the case where an actually measured current exceeds the target peak current Ipeak, the valve-opening voltage (boosted high voltage) VH is recurrently and slightly decreased until the actually measured current and the target peak current Ipeak coincide with each other. In the case where the actually measured current is smaller than the target peak current Ipeak, the valve-opening voltage (boosted high voltage) VH is recurrently and slightly increased until the actually measured current and the target peak current Ipeak coincide with each other. In other words, control is performed in such a way that the predetermined peak current Ipeak can always be obtained at a time when the predetermined circuit-closing drive time Th has elapsed, so that the valve-opening control accuracy is raised.
According to FIGS. 2 through 5 and 7 in Patent Document 3, listed below, a fuel supply system is provided with a microprocessor 24 that generates a valve opening signal 24a and a holding signal 24b, a voltage boosting circuit 32, switches 33, 34, 36, and 37, an upstream current detectors 53 and 56, a downstream current detector 63, a control unit 39, and a diagnosis unit 41; the control unit 39 performs rapid excitation control in response to the valve opening signal 24a and the holding signal 24b generated by the microprocessor 24 and a signal voltage proportional to a rapid excitation current obtained through the upstream current detectors 53; the diagnosis unit 41 measures an elapsed time T2 in which the rapid excitation current reaches a predetermined peak current 71, and in the case where the elapsed time T2 is too short, the diagnosis unit 41 determines that there exists a shortcircuit abnormality in an electromagnetic coil 13 or a short-to-ground abnormality of the positive line and reports the determination to the microprocessor 24 through serial communication 24c.